This invention pertains to a method of treatment of a metal substrate to provide a corrosion-resistant surface thereon, and to the resulting corrosion-inhibited product of this method. This invention pertains particularly to this method as applied to an iron or steel substrate and as applied to non-ferrous substrates such as copper and zinc.
A wide variety of coating materials and treating methods are known for providing a corrosion-resistant surface on a metallic substrate. Among these are various anodization methods. Iron and steel, for example, may be anodized in a borate bath to impart some degree of corrosion resistance to the metal surface. Such treatments may also be combined with other coatings, such as chromate deposition, to enhance the corrosion resistance of the treated surface. Further, an organic compound, namely glycerin, has also been included in such baths, apparently as a reducing agent for the chromate (see U.S. Pat. Nos. 2,733,199--Wick and 3,296,106--Smith et al). Other known patents disclosing a sodium borate anodization bath are:
U.S. Pat. No. 2,063,197--Schneidewind PA0 U.S. Pat. No. 2,312,076--Cook et al PA0 U.S. Pat. No. 2,780,592--Wick et al PA0 U.S. Pat. No. 2,901,409--De Long PA0 U.S. Pat. No. 2,926,125--Currah et al PA0 U.S. Pat. No. 3,180,807--Quinn PA0 U.S. Pat. No. 3,264,201--Schink et al PA0 U.S. Pat. No. 3,400,058--Ross et al PA0 U.S. Pat. No. 3,477,921--Sanford PA0 U.S. Pat. No. 3,772,165--Yamagishi et al PA0 U.S. Pat. No. 4,209,366--Leroy et al PA0 Step I Anodization at +1.0V vs. SCE in 0.15M borate solution (pH=8.4) for 10 minutes. PA0 Step II Anodization at +1.4V vs. SCE in 0.004M 8-hydroxyquinoline (HO) -0.15M borate solution (pH=8.4) for 10 minutes. PA0 Step 1-Anodication at E.sub.a.sbsb.1 =+1.0V vs. SCE in a 0.15M borate solution (pH=8.4) for 10 minutes. PA0 Step 2-Anodization at E.sub.a.sbsb.2 =+1.4V vs. SCE in 0.004M 8-hydroxyquinoline (HO) -0.15M borate solution (pH=8.4) for 10 minutes.
Weisstuch et al., in an article published in Mater. Prot. Perform., 10(4), 11(1971), describe attempted corrosion inhibition of iron by 8-hydroxyquinoline in a corrosion medium simulating cooling water at pH 7 and the formation of an insoluble nonadherent film.
Nicki et al., in an article published in J. Electrochem. Soc. 122, 855(1975), describe a nonadherent copper/8-hydroxyquinoline chelate formed by anodizing copper in an acetate buffer solution containing 8-hydroxyquinoline.
None of these patents and publications, however, appear to disclose the incorporation of any other organic compound in an electrolytic anodization or corrosion resistance-imparting bath, particularly in combination with a borate electrolyte and particularly not including any organic compound known for its ability to form an adherent complex with the underlying metal substrate, and most particularly not including a two-step process for forming a corrosion inhibited product.
The treatment of metal surfaces to retard or prevent corrosion is of great economic interest: thus there is a continuing need for ever more effective corrosion-resistant treatment methods and products of those methods.
It is, therefore, the general object of the present invention to provide a new corrosion inhibiting metal surface treatment method and the new product thereof.